1. Field of Invention
The technical scope of the invention is that of igniting devices for a propellant charge contained within a cylindrical case of a piece of ammunition.
The invention is more particularly aimed at igniting devices implementing at least one linear energetic igniting element, such as a detonating cord.
2. Description of Related Art
Such igniting devices are known, notably by patents U.S. Pat. No. 5,325,785 and U.S. Pat. No. 5,129,324.
In making cased munitions of whatever calibre conventional priming tubes (such as those described for example in patent FR2593905) are tending to be replaced by linear energetic elements. These elements allow ignition to be optimised for modern munitions that are of substantial length and/or a volume of powder that is difficult for the flame of a conventional primer to reach, such as that arranged, for example, around the tail piece of a projectile.
These energetic elements are connected to a common ignition means and they enable the multi-point ignition of the propellant charge.
These elements are made, for example, in the shape of wires, films, strands, cords. They comprise, for example, a pyrotechnic composition, such a black powder or a composition combining boron with potassium nitrate or else aluminium and potassium perchlorate, or magnesium/polytetrafluorethylene/copolymer of chlorofluoroethylene (magnesium/Teflon (trade mark)/Viton (trade mark).
The composition is packaged in a support made, for example, of a tube of plastic material.
The energetic elements can also comprise one or several secondary explosives (cyclonite, homocylconite) made integral with a support.
According to the energetic material used, the ignition will be propagated more or less quickly (reaction of combustion, deflagration or detonation) and the radial effectiveness of the ignition ensured by the energetic element will also be more or less good.
According to the munition, the energetic elements are fastened to the inner surface of the, case or to a rear part of the projectile.
With such ignition devices there is the problem of setting them into place inside the munition case and notably that of making the different energetic elements integral with a common ignition means, for example an axial primer fastened to a base of a munition case.
Indeed, in traditional munitions, the propellant charge is generally arranged in the case before the primer tube is set into position. The latter is introduced last via an axial hole in the base and is fastened simply by screwing. Such a solution is not adapted to an ignition device that incorporates different elements evenly spaced inside the case.
To overcome this problem, patent U.S. Pat. No. 5,325,785 proposes the provision of a detonating cord support that caps the rear of the projectile and onto which an ignition support is screwed.
Such a solution, nevertheless, has certain drawbacks.
First of all the cord support is a part that encompasses the rear of the projectile at its tail end. This part is complicated in shape, and incorporates longitudinal grooves receiving the cords and other grooves co-operating with the tail fins.
It is not easy to set this part into position, notably when the cords are integral with the inner surface of the case.
Such a solution may be only adopted when the tail piece of the projectile is very close to the base of the case. Moreover, such a holding part that is integral with the projectile runs the risk of perturbing its ballistic performances.
The aim of the invention is to propose an ignition device that does not suffer from such drawbacks.
The ignition device proposed by the invention is both simple and inexpensive and facilitates the operations of loading the powder and assembling the case.
It can be easily adapted to any type of munition whatever the length of the, projectile, with or without tail fins.
Thus, the subject of the invention is an ignition device for a propellant charge contained in a cylindrical case of a munition, said device comprising at least one linear energetic element and means to ignite said element, and characterised in that the ignition means comprise a tubular part, placed at a bottom cap part of the case and delimiting a chamber that communicates with a pyrotechnic igniting component, said tubular part comprising an axial hole intended to allow the passage and entry into the chamber of the linear igniting element or elements arranged substantially along the case axis.
The ignition device according to the invention can incorporate at least two linear energetic ignition elements, said elements being connected along at least part of their length so as to form a strand that is placed substantially along the case axis and penetrates into the chamber of the tubular part through the axial hole.
The chamber can enclose at least one ring-shaped ignition relay.
The axial hole of the tubular part can have a diameter that is substantially the same as that of the strand.
Advantageously, the strand can be of a length greater than or equal to 50 mm.
The strand can penetrate into the tubular part over a length of at least 15 mm.
The energetic linear ignition element or elements can be fastened at a rear part of a projectile placed in the case.
The energetic linear ignition elements can alternatively be fastened onto an inner cylindrical surface of the case.
The tubular part can be made of a combustible and/or energetic material.
The ignition means can comprise an igniter unit onto which the tubular part will be fastened, said igniter unit comprising a pyrotechnic igniting component, such a squib, and at least one ignition relay.
The tubular part can be integral with a cup that obturates the bottom of the case and that is made integral with a cylindrical wall of the case by fastening means.